1. Field of the Invention
The invention relates to an actuating drive for automatically actuating a friction clutch.
2. Description of the Prior Art
German reference DE 43 09 901 A1 discloses a hydraulic actuating drive by means of which a friction clutch and a shift transmission may be actuated in an automated manner. For automated clutch actuation, a transmitter cylinder which is operationally connected to a receiver cylinder has pressure applied to it. The receiver cylinder, for its part, is operationally connected to the clutch release of the friction clutch. By means of applying pressure to the transmitter cylinder, the actuating movement of the latter being detected by means of a sensor, the friction clutch may be actuated in an automated manner. The pressure necessary for the actuation of the transmitter cylinder is provided by a pressure reservoir or store, it being possible to regulate the connection between transmitter cylinder and pressure store by means of a valve unit. The valve unit provided has pulsed switching valves or a proportional directional valve.
Assigned to the pressure store are at least two further valve units, via which pressure may be applied to two actuating cylinders for automated actuation of the shift transmission. The valve units provided are proportional directional valves, pressure-regulating valves or pulsed switching valves. The actuating movement of these actuating cylinders is in each case detected directly or indirectly by means of sensors. For the purpose of actuation in the gear selection direction, a double-acting cylinder is provided. For the remaining actuating cylinders, it is also possible for single-acting cylinders to be provided. For the purpose of controlling the automated friction clutch and for the automated actuation of the shift transmission, the hydraulic actuating drive is assigned a control device to which the signals from the sensors assigned to the actuating cylinder and further signals characterizing the operating state of the vehicle are fed.
WO 96/23 671 discloses an arrangement by means of which a clutch and a transmission may be actuated automatically. The arrangement comprises a main valve by means of which, for automatic actuation of the clutch or for automatic actuation of the transmission, the application of pressure to an actuating unit in each case assigned to the clutches or to the transmission may be enabled.